It should be of no surprise to today's urban dwellers that many services are delivered to their homes through hidden conduits buried beneath the ground surface. Electric power, telephone, and television services are now carried through buried cables in many areas. Of course, water and sewer services have traditionally used subsurface flowlines. For authorized repair and extension of service, access to these underground conduits is periodically required.
The excavation of narrow trenches in the soil surface to approach, or install, subsurface utility conduits has always been troublesome. In the past, hand implements such as shovels, picks, and hoes were utilized for this purpose when sufficient manpower was available. Now, however, machine-driven devices are frequently employed in large-scale commercial projects. Nevertheless, these prior art tools have proven to be less than optimal for digging narrow trenches being a few inches in width around human abodes.
When using even the narrowest shovel and hoe blades, more soil is often relocated in excavating an earthen trench than is absolutely necessary. Not only is time and energy wasted in using such tools, but the scar remaining upon the surface of the ground, after backfilling of the trench has been completed, is often unnecessarily large. The alternative, powered trenching machines, cannot be moved into confined areas where utility conduits are frequently placed and are very costly to operate.
It is known that many hand tools including loop-type blades only minimally disturb the soil through which the blades are drawn. Generally, however, the blades of the prior art tools include little more than a substantially rigid loop or band, formed from metallic sheet material and secured to the end of a wooden handle. These bands are frequently narrow in width so that the distance between the opposed cutting edges thereof are on the order of 1 inch (2.5 centimeters) apart. Although ideal for severing near-surface roots with minimal resistance, the prior art blades are not particularly helpful in excavating substantial volumes of earthen material from a trench.
It has been found that by increasing the width of a loop-type blade, its ability to move and carry soil can be increased dramatically without appreciably raising drag forces induced while such is moved through the soil. Sandy soils, for instance, have an angle of repose of approximately 34 degrees making it difficult for the narrow, prior art blades to retain but a small volume of soil material thereon. Thus, a prior art blade having a 1 inch (2.5 centimeter) width is capable of supporting only 0.36 cubic inches (5.9 cubic centimeters) of soil per inch of blade length. However, a tubular or loop-type blade having a 6 inch (15 centimeter) width, heretofore unseen in the prior art, is theoretically capable of retaining 13 cubic inches of soil per inch of blade length. A need, therefore, exists for a trenching tool having a the benefits of a loop-type blade, yet having dimensions sufficiently capable of digging, and rapidly removing relatively large volumes of spoil material from, an earthen excavation.